Without limiting the scope of the invention, the background of the invention is described in connection with fans used in cooling towers. Cooling towers are heat rejection devices that extract waste heat to the atmosphere through the cooling of a water stream to a lower temperature. The heat from the water stream transferred to the air stream raises the air's temperature and its relative humidity to 100%, and this air is discharged to the atmosphere. Cooling towers are commonly used to provide cooled water for air-conditioning, manufacturing and electric power generation. Depending on the application, cooling towers can handle water streams of only a few gallons of water per minute supplied in small pipes up to hundreds of thousands of gallons per minute supplied in pipes as much as 15 feet (about 5 meters) in diameter.
As shown in FIGS. 1A and 1B, cooling towers 100 and 150 include a fan 102 that is used to draw air 104 from air inlets 106 through a fill area 108 and exhaust the heated and moist air 110 to the atmosphere. The heated water enters the cooling tower 100 and 150 via water inlets 112 that direct the heated water over the fill area 108 so that the water is cooled by the air. The cooled water is then collected and returned to the facility via water output 114. Although the design of any specific cooling tower may vary, the principles illustrated in FIGS. 1A and 1B are applicable.
The fan 102 operates in a very corrosive environment as a result of the high moisture content, velocity and elevated temperature of the air passing over the fan 102. Moreover, the moisture in the air may also contain various contaminants. Fan vibration and noise are also important operational considerations. As shown in FIG. 2, fan 102 includes a set of fan blades 200 (typically at least six) connected to a fan hub 202. The fan hub 202 is connected to a speed reducer or gearbox 206 via shaft 204. The speed reducer or gearbox 206 is connected to a motor 210 via drive connection (shaft) 208. The speed reducer or gearbox 206 is required in most cases to provide the desired torque and fan blade RPMs. For example, the fan 102 can be an adjustable multi-blade design having a minimum of six (6) fiberglass reinforced epoxy (FRE) fan blades 200 rotating at a tip speed of less than 11,000 FPM and a fan hub 202 of HDG steel plate construction. A non-corrosive metal spacer sleeve may also be provided to prevent the fan 102 from dropping onto speed reducer 206 in the event of shaft bushing failure. The speed reducer or gearbox 206 is typically of the spiral bevel, single (or double) reduction type. In addition, the speed reducer or gearbox 206 is typically bolted to a stainless steel base plate which in turn is bolted and grouted to the concrete structure. The fan motor 210 is close-coupled to the speed reducer or gearbox 206 by means of an elastomeric type coupling. The fan motor 210 is typically a three phase corrosive duty motor suitable for across line starting that is mounted to a stainless steel base plate, bolted and grouted securely to the concrete fan deck. If the fan motor 210 is located outside of the airstream, a drive connection or shaft 208 (e.g., stainless steel, full-floating type, with non-lubricated flexible couplings at both ends) is used to connect the motor 210 to the speed reducer or gearbox 206. A galvanized steel or composite guard or shaft type can also be used to prevent damage to surrounding equipment in case of shaft failure.
The fan assembly (fan 102, speed reducer or gearbox 206 and motor 210) having many moving parts that require maintenance and are prone to failure, especially when operated in the harsh environment of a cooling tower. Moreover, the installation of the fan assembly is difficult and time consuming because of the operating tolerances that must be maintained in order to align the various drive components and reduce vibration and noise.
As a result, there is a need for a system and apparatus for driving a fan that reduces the downtime caused by failures or maintenance, provides increased efficiency and reliability, and provides greater operational control.